Merge pull request #2751 from vibe-d/fix_freelist_ref_gc_leak

Also destroy the end callback stream in HTTPClientResponse deterministically

http/vibe/http/client.d

@@ -1259,6 +1259,7 @@ final class HTTPClientResponse : HTTPResponse {
 		auto cli = m_client;
 		m_client = null;
 		cli.m_responding = false;
+		destroy(m_endCallback);
 		destroy(m_zlibInputStream);
 		destroy(m_chunkedInputStream);
 		destroy(m_limitedInputStream);